E10
東日本大震災時に発生した葉ノ木平地すべりの発生・運動機構に対するダイナミック検証
Dynamic examination of the initiation and movement mechanisms of Hanokidaina landslide from
the 2011 off the Pacific coast of Tohoku Earthquake
○王功輝・末峯章・秦吉弥・釜井俊孝
○Gonghui WANG, Akira SUEMINE, Yoshiya HATA, Toshitaka KAMAI
A flow type landslide (1×105 m3) was triggered on Hanokidaira area by 2011 off the Pacific coast of Tohoku Earthquake, killing more than 10 people. The slope consists of pyroclastic flow deposits that were formed at different times, with a layer of paleosol that was outcropped. Above the paleosol there is a layer of pumice and scoria, which is very rich in natural moisture content (~145%). From field observation, we inferred that the sliding surface originated on the boundary between the paleosol layer and the layer of pumice and scoria. To examine the possible trigger and movement mechanism of these landslides, we monitored the aftershocks on landslide area, and inferred the possible seismic response of the landslide area during the main shock. We took samples from both layers, and performed undrained seismic loading tests on them by using the inferred seismic movement during the main shock. During the tests, the samples were prepared in saturated state or in natural water content state. The results showed that shear failure could be triggered by the inferred seismic movement, and high pore-water pressure could be generated after failure, resulting in great loss in the shear strength. Therefore, we concluded that site-based seismic movement enabled the initiation of the hill slope and high water content in soil layer enabled the generation of high pore-water pressure along the shear zone (sliding surface), resulting in the high mobility of this landslide.
